Devices and methods for removal of acute blockages from blood vessels

ABSTRACT

A clot retrieval device comprises an elongate shaft  104  and an expandable clot retrieval element  2101  on the shaft, the clot retrieval element comprising a framework formed from a substrate material such as Nitinol and having a plurality of struts  2105  and crowns  2102 , at least some of the struts  2105  comprises at least one widened portion  2104  of the substrate material to provide enhanced radiopacity. The framework is coated with a radiopaque material such as gold. The device is rendered radiopaque with reduced damping effects.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase entry under 35 U.S.C. § 371 of International PCT Application No. PCT/EP2014/054828, filed on Mar. 12, 2014, which claims priority to U.S. Provisional Application No. 61/784,940, filed on Mar. 14, 2013.

FIELD OF THE INVENTION

This invention relates to devices intended for removing acute blockages from blood vessels. The invention especially relates to means of rendering such devices visible under x-ray or fluoroscopy. Acute obstructions may include clot, misplaced devices, migrated devices, large emboli and the like. Thromboembolism occurs when part or all of a thrombus breaks away from the blood vessel wall. This clot (now called an embolus) is then carried in the direction of blood flow. An ischemic stroke may result if the clot lodges in the cerebral vasculature. A pulmonary embolism may result if the clot originates in the venous system or in the right side of the heart and lodges in a pulmonary artery or branch thereof. Clots may also develop and block vessels locally without being released in the form of an embolus—this mechanism is common in the formation of coronary blockages. The invention is particularly suited to removing clot from cerebral arteries in patients suffering acute ischemic stroke (AIS), from coronary native or graft vessels in patients suffering from myocardial infarction (MI), and from pulmonary arteries in patients suffering from pulmonary embolism (PE) and from other peripheral arterial and venous vessels in which clot is causing an occlusion.

BACKGROUND

Clot retrieval devices comprising a self-expanding Nitinol stent-like member disposed at the end of a long shaft are commonly used to remove clot from blood vessels, particularly from patients suffering from acute ischemic stroke. These devices are typically provided with small marker bands at either end of the self-expanding member which help to indicate the device's position. It would be very beneficial to a physician to be able to see the full expandable body of such a device under fluoroscopy, and thus receive visual information on the device's condition as rather than simply its position. Clot retrieval procedures are conducted under an x-ray field in order to allow the user visualise the anatomy and at a minimum the device position during a procedure. It is desirable, and enhances the user experience to be able to visualise the device state as well as position structure during a procedure, for example if the device is in an expanded configuration or a collapsed configuration. This means that the radiopaque sections must move closer to the device axis in a collapsed configuration and further from a device axis in an expanded configuration. It is generally desirable to make interventional devices such as clot retrieval devices more flexible and lower profile to improve deliverability in interventional procedures. This may be achieved by reducing the dimensions for device features, and the level of contrast seen under x-ray is generally reduced as the device dimensions are reduced. Radiopaque materials generally comprise noble metals such as gold, tantalum, tungsten, platinum, iridium and the like, and generally have poor elastic recovery from a strained condition and are therefore not optimal material for devices, particularly for the regions of these devices undergoing high strain in moving from a collapsed to an expanded state and vice versa. Radiopaque materials may be added through coating a structure comprising a highly recoverable elastic material such as Nitinol, but coating the entire structure has a dampening effect that inhibits device performance.

This invention overcomes limitations associated with the dampening effect of adding radiopaque material to an expandable clot retrieval device, while making the structure sufficiently radiopaque to allow full visualisation of the device condition as well as position.

STATEMENT OF THE INVENTION

Various devices and method are described in our PCT/IE2012/000011 which was published under the number WO2012/120490A. This PCT application claims the benefit of U.S. Provisional 61/450,810, filed Mar. 9, 2011 and U.S. Provisional 61/552,130 filed Oct. 27, 2011. The corresponding U.S. National stage is U.S. application Ser. No. 13/823,060 filed on Mar. 13, 2013. The entire contents of all of the above-listed applications are herein incorporated by reference.

This invention is particularly applicable to clot retrieval devices comprising expandable bodies made from a metallic framework. Such a framework might be a Nitinol framework of interconnected struts, formed by laser (or otherwise) cutting a tube or sheet of material, and may thus comprise a structure with a pattern of strut features and connector features. In some embodiments the clot retrieval device may comprise an inner expandable member and an outer expandable member, which may define a flow lumen through a clot and engage a clot.

In order to go from a collapsed to an expanded configuration, portions of the device undergo recoverable deformation and varying levels of strain. Some portions require a higher level of recoverable strain than others in order to work effectively. Where the framework or expandable member comprises a pattern of strut features and connector features, the struts typically comprise inflection regions or connection regions generally referred to as crowns, which typically experience higher strain than the struts or connectors when the device is collapsed or expanded.

The term detector is generally referred to as the part of the equipment which collects the beam for processing into useful images, and can include for example flat panel detectors or image intensifiers. X-ray beams are filtered through an anti-scatter grid during processing. This filters out scattered beams which deflect significantly from the trajectory of the source beam, and beams less significantly deflected off the original trajectory pass through the anti-scatter grid creating areas of overlap between non-scattered photon beams and scattered photon beams, referred to herein as shadow areas.

In an embodiment of this invention discrete markers are placed in low strain regions of the clot retrieval device members, and high strain regions comprise a super elastic material with little or no radiopaque material.

In use, it is desirable to maximise visibility and therefore maximise the area and volume of radiopaque markers located in the clot retrieval device. Increasing the ratio of radiopaque material to Nitinol generally improves radiopacity. For the effective operation of the device in moving between expanded and collapsed configurations, it is desirable to maintain a ratio of Nitinol to radiopaque material such that strain levels from an expanded to a collapsed configuration are substantially in the elastic region. This creates a conflict of requirements, and the solutions provided herein overcome this conflict.

Discrete markers placed in close proximity create overlapping shadow areas, referred to as intersection zones herein, which give the illusion under x-ray imaging of a continuous marker thereby providing fuller visual information to the user in an x-ray image.

Various embodiments of the invention are described in more detail below. Within these descriptions various terms for each portion of the devices may be interchangeably used. Each of the described embodiments are followed by a list of further qualifications (preceded by the word “wherein”) to describe even more detailed versions of the preceding headline embodiment. It is intended that any of these qualifications may be combined with any of the headline embodiments, but to maintain clarity and conciseness not all of the possible permutations have been listed.

According to the invention there is provided a clot retrieval device comprising an elongate shaft and an expandable clot engaging element on the shaft, the clot engaging element comprising a framework formed from a substrate material and having a plurality of struts and crowns, at least some of the struts comprising at least one widened portion of the substrate material to provide enhanced radiopacity.

In one embodiment the strut comprises a plurality of widened portions which are spaced-apart along a length of the strut.

The widened portion of the strut may be at least 50%, optionally at least 75%, optionally at least 100%, optionally at least 125%, optionally at least 150%, optionally at least 175%, optionally at least 200%, optionally at least 300% wider than the regions along the length of the strut between the widened portions.

The widened portions may have a length which is less than 100%, optionally less than 75%, optionally less than 50%, optionally less than 25% of the length of the regions of the strut between the widened portions.

The length of the regions of the strut between the widened portions may be greater than 300%, optionally greater than 400%, optionally greater than 500%, optionally greater than 600%, optionally greater than 700%, optionally greater than 800%, optionally greater than 900% of the width of the strut.

In one embodiment the clot engaging element is cut from a tube of uniform thickness.

In one embodiment wherein at least a portion of the framework is coated with a radiopaque material.

In one embodiment the substrate material is a superelastic material such as Nitinol or other super or pseudo elastic metallic alloy.

In one case the coating material is Gold, Tantalum, Tungsten, Platinum or an alloy of one of these elements or other dense element or alloy containing one or more radiodense elements.

In one embodiment the coating material comprises a polymer or adhesive filled with a dense or high atomic number material such as Barium Sulphate, Bismuth SubCarbonate, Barium OxyChloride, Gold, Tungsten, Platinum or Tantalum.

In one case the coating material is applied using an electroplating process, a dipping process, a plasma deposition process, an electrostatic process, a dip or spray coating process, a sputtering process, a soldering process, a cladding process or a drawing process.

The substrate material may have a density of less than 10 g/cm³, less than 8 g/cm³.

The coating material may have a density of more than 10 g/cm³, more than 15 g/cm³, more than 18 g/cm³.

One embodiment of a device of this invention comprises a clot retrieval device comprising an elongate shaft and an expandable section, the expandable section comprising a framework of interconnected strut elements, the connection region between adjacent strut elements comprising crown elements, said framework formed from a substrate material, at least a portion of a plurality of said strut elements coated with a coating material, and at least a portion of a plurality of said crown elements not coated with said coating material.

The substrate material may have a density of less than 10 g/cm³, less than 8 g/cm³.

The coating material may have a density of more than 10 g/cm³, more than 15 g/cm³, more than 18 g/cm³.

In one embodiment the substrate material is a superelastic material such as Nitinol or other super or pseudo elastic metallic alloy.

In one case the coating material is Gold, Tantalum, Tungsten, Platinum or an alloy of one of these elements or other dense element or alloy containing one or more radiodense elements.

In one embodiment the coating material comprises a polymer or adhesive filled with a dense or high atomic number material such as Barium Sulphate, Bismuth SubCarbonate, Barium OxyChloride, Gold, Tungsten, Platinum or Tantalum.

In one case the coating material is applied using an electroplating process, a dipping process, a plasma deposition process, an electrostatic process, a dip or spray coating process, a sputtering process, a soldering process, a cladding process or a drawing process.

Another aspect of this invention comprises a method of manufacturing the expandable body of a clot retrieval device, the expandable body comprising a substrate material and a coating material, the method comprising:

-   -   a first step of applying the coating material to the substrate         material,     -   a second step of removing at least a portion of said coating         material from at least one area of said substrate material,     -   and a third step of cutting away regions of both coating and         substrate material to form an interconnected pattern of coated         and uncoated regions.

In one embodiment the first step comprises an electroplating process, a dipping process, a plasma deposition process, an electrostatic process, a dip or spray coating process, a sputtering process, a soldering process, a cladding process or a drawing process.

In one case the second step comprises a grinding process, a polishing process, a buffing process, an etching process, a laser cutting or laser ablation process.

In one embodiment the third step comprises a laser cutting process, a wire cutting process, a water jet cutting process, a machining process or an etching process.

In one case the coating material is Gold, Tantalum, Tungsten, Platinum or an alloy of one of these elements or other dense element or alloy containing one or more radiodense elements.

In one embodiment the coating material comprises a polymer or adhesive filled with a dense or high atomic number material such as Barium Sulphate, Bismuth SubCarbonate, Barium OxyChloride, Gold, Tungsten, Platinum or Tantalum.

In one case the substrate material comprises Nitinol, or an alloy of Nitinol or another super or pseudo elastic alloy.

In one embodiment the interconnected pattern comprises a plurality of strut elements and connector elements.

In one case the interconnected pattern of the clot retrieval device comprises an expanded state and a collapsed state.

In one embodiment the second step removes at least a portion of the coating from those areas of the interconnected pattern which experience the highest strain in moving from the expanded state to the collapsed state, and/or from the collapsed state to the expanded state.

In one case the strut elements terminate in crown elements.

In one embodiment the second step removes some or all of the coating from the crown elements.

In one case the second step removes some or all of the coating from discrete sections of the strut elements; in one embodiment these discrete sections comprising stripes across the width of the struts.

Another embodiment of a device of this invention comprises a clot retrieval device comprising an elongate shaft and an expandable section, the expandable section formed from a substrate material, at least a portion of the substrate material coated with a first coating material and at least a portion of the first coating material coated with a second coating material.

In one case the substrate material is a superelastic material such as Nitinol or other super or pseudo elastic metallic alloy.

In one embodiment the first coating material is Gold, Tantalum, Tungsten, Platinum or an alloy of one of these elements or other dense element or alloy containing one or more radiodense elements.

In one case the first coating material is applied by a plasma deposition process, an electrostatic process, a dip or spray coating process, a sputtering process, a sputtering process using a cylindrical magnetron, a soldering process, a cladding process or a drawing process.

In one embodiment the first coating material comprises a porous or non-porous columnar structure.

In one case the first coating material comprises a porous columnar structure, comprising generally independent columns of the coating material which extend substantially perpendicularly to the substrate surface.

In one embodiment said columns have a first end and a second end, said first end being adjacent the substrate surface, and the spacing between the second ends of adjacent columns varying with deformation of the substrate material/expandable body.

In one case the second ends of the first coating material define an outer surface, and said outer surface is a rough surface.

In one embodiment the second coating material comprises a smooth surface, and/or a soft surface. In one case the second coating material is a polymeric material.

In one embodiment the elastic modulus of the second coating material is lower than that of the first coating material.

In one case the elastic modulus of the second coating material is lower than that of the substrate material.

In one embodiment the elastic modulus of the second coating material is less than 50% of that of the first coating material and/or substrate material.

In one case the elastic modulus of the second coating material is less than 40% of that of the first coating material and/or substrate material.

In one embodiment the elastic modulus of the second coating material is less than 30% of that of the first coating material and/or substrate material.

In one case the elastic modulus of the second coating material is less than 20% of that of the first coating material and/or substrate material.

In one embodiment the elastic modulus of the second coating material is less than 10% of that of the first coating material and/or substrate material.

In one case the second coating material is a hydrophilic material or a hydrogel.

In one embodiment the coefficient of friction of the first coating material is greater than 0.2, greater than 0.3, greater than 0.4, greater than 0.5.

In one embodiment the coefficient of friction of the second coating material is less than 0.2, less than 0.15, less than 0.1, less than 0.08.

Another embodiment of a device of this invention comprises a clot retrieval device comprising an elongate shaft and an expandable member, the expandable member comprising a proximal section, a body section and a distal section, the body section comprising a metallic framework of a first (or substrate) material, the metallic framework comprising a plurality of strut elements, said strut elements comprising an outer surface, an inner surface and side wall surfaces, at least one of said surfaces comprising a smooth surface and recessed features, at least some of said recessed features at least partially filled with a second (coating) material.

In one embodiment the recessed features comprise grooves or slots in the top surface of a strut element.

In one case the recessed features comprise holes in the top surface of a strut element.

In one embodiment the recessed features comprise holes through a strut element.

In one case the above holes are circular, or oblong, or square or rectangular.

In one embodiment the recessed features comprise grooves or slots in the side wall of a strut element.

In one case all of the recessed features are filled with the second (coating) material.

In one embodiment at least one of the smooth surfaces are coated with the second (coating) material.

In one case all of the smooth surfaces are coated with the second (coating) material.

In one embodiment the thickness of coating material in the recessed features is greater than the thickness of coating material on the smooth surfaces.

Another aspect of this invention comprises a method of manufacturing the expandable body of a clot retrieval device, the expandable body comprising a substrate material and a coating material, the method comprising: a first step of removing material from discrete areas of the substrate material to form recesses, a second step of applying the coating material to the substrate material and recesses, and a third step of removing some or all of the coating from the non-recessed areas of the substrate.

Another aspect of this invention comprises a method of applying a radiopaque coating to selective areas of the expandable body of a clot retrieval device, the method involving a masking material and comprising:

-   -   a first step of applying a masking material to selective areas         of the expandable body,     -   a second step of applying a coating material to the expandable         body,     -   and a third step of removing the masking material from the         expandable body.

Another aspect of this invention comprises a method of manufacturing the expandable body of a clot retrieval device, the expandable body comprising a substrate material and a coating material, the method involving a masking material and comprising:

-   -   a first step of applying the masking material to the substrate         material,     -   a second step of removing at least a portion of said masking         material from at least one area of said substrate material,     -   a third step of cutting away regions of both masking and         substrate material to form an expandable body with masked and         unmasked regions,     -   a fourth step of applying a coating material to the expandable         body, such that the coating material adheres to the unmasked         areas but does not adhere to the masked areas of the expandable         body,     -   and a fifth step of removing the masking material from the         expandable body.

In one embodiment the fourth step comprises an electroplating process, a dipping process, a plasma deposition process, an electrostatic process, a dip or spray coating process, a sputtering process, a soldering process, a cladding process or a drawing process.

In one case the second step comprises a grinding process, a polishing process, a buffing process, an etching process, a laser cutting or laser ablation process.

In one case the third step comprises a laser cutting process, a wire cutting process, a water jet cutting process, a machining process or an etching process.

In one embodiment the coating material is Gold, Tantalum, Tungsten, Platinum or an alloy of one of these elements or other dense element or alloy containing one or more radiodense elements.

In one case the coating material comprises a polymer or adhesive filled with a dense or high atomic number material such as Barium Sulphate, Bismuth SubCarbonate, Barium OxyChloride, Gold, Tungsten, Platinum or Tantalum.

In one embodiment the substrate material comprises Nitinol, or an alloy of Nitinol or another super or pseudo elastic alloy.

In one case the expandable body comprises a plurality of strut elements and connector elements.

In one embodiment the expandable body of the Clot Retrieval device comprises an expanded state and a collapsed state.

In one case the third step results in the masking material being positioned on those areas of the expandable body which experience the highest strain in moving from the expanded state to the collapsed state, and/or from the collapsed state to the expanded state.

Another embodiment of a device of this invention comprises a clot retrieval device comprising an expandable body and an elongate shaft, the expandable body comprising a proximal section, a body section and a distal section, the body section comprising a framework of strut elements and at least one fibre assembly, the fibre assembly comprising a radiodense material.

In one embodiment the distal section comprises a clot capture scaffold.

In one case the clot capture scaffold comprises a net.

In one embodiment the fibre assembly comprises at least one fibre and at least one floating element, the floating element comprising a radiodense material.

In one case the fibre comprises a polymer monofilament, or plurality of polymer filaments.

In one embodiment the polymer filament is of LCP, Aramid, PEN, PET, or UHMWPE.

In one case the fibre comprises at least one metallic filament.

In one embodiment the metallic filament is a nitinol wire, or plurality of such wires.

In one case the metallic filament comprises a nitinol outer layer with an inner core of a radiodense material such as Gold, Platinum, Tantalum or Tungsten.

In one embodiment the floating element is a coil, a tube, or a bead.

In one case the material of the floating element comprises Gold, Tantalum, Tungsten, Platinum or an alloy of one of these elements or other dense element or alloy containing one or more radiodense elements.

In one embodiment the material of the floating element comprises a polymer filled with a dense and/or high atomic number material such as Barium Sulphate, Bismuth SubCarbonate, Barium OxyChloride or Tantalum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a clot retrieval device of the invention;

FIG. 2a is an isometric view of a portion of a clot retrieval device comprising standard material under x-ray imaging;

FIG. 2b is a representation of an x-ray image of FIG. 2 a;

FIG. 2c is an isometric view of a portion of another clot retrieval device comprising a radiopaque material under x-ray imaging;

FIG. 2d is a representation of an x-ray image of FIG. 2 c;

FIG. 3a is an isometric view of a portion of another clot retrieval device comprising standard material and radiopaque material under x-ray imaging;

FIG. 3b is a representation of an x-ray image of FIG. 3 a;

FIG. 4a is a cross section view of a strut feature of a clot retrieval device comprising standard material and radiopaque material;

FIG. 4b is a representation of an x-ray image of FIG. 4 a;

FIG. 5 schematically represents the resulting x-ray image from two adjacent shadow zones;

FIG. 6a is a cross section of a strut feature of a clot retrieval device comprising standard material and spaced apart radiopaque material features;

FIG. 6b is the a representation of an x-ray image from FIG. 6 a;

FIG. 7a is an isometric view of a portion of a clot retrieval device;

FIG. 7b is a developed plan view of the portion of a clot retrieval device from FIG. 7 a;

FIG. 8 is a developed plan view of a portion of another clot retrieval device;

FIG. 9 is a developed plan view of a portion of another clot retrieval device;

FIG. 10a is a view of a portion of a clot retrieval device;

FIG. 10b is a detail view of a region of the device shown in FIG. 10 a;

FIG. 10c is an isometric view of the device shown in FIG. 10 a;

FIG. 11 is an isometric view of a portion of a clot retrieval device;

FIG. 12 is an isometric view of a portion of a clot retrieval device;

FIG. 13a is an isometric view of a tube used to form a part of a clot retrieval device;

FIG. 13b is an isometric view of a tube used to form a part of a clot retrieval device;

FIG. 14 is an isometric view of a portion of a clot retrieval device;

FIG. 15 is an isometric view of a portion of a clot retrieval device;

FIG. 16 is an isometric view of a portion of a clot retrieval device;

FIG. 17a is a side view of an element of a clot retrieval device;

FIG. 17b is a view of the element shown in FIG. 17a in bending;

FIG. 18a is a side view of an element of a clot retrieval device;

FIG. 18b is a view of the element shown in FIG. 18a in bending;

FIG. 19a is a stress-strain curve of a material used in the construction of a clot retrieval device;

FIG. 19b is a stress-strain curve of another material used in the construction of a clot retrieval device;

FIG. 19c is a stress-strain curve of an element of a clot retrieval device;

FIG. 19d is a stress-strain curve of another element of a clot retrieval device;

FIG. 20a is a side view of part of a clot retrieval device;

FIG. 20b is a side view of part of a clot retrieval device;

FIG. 20c is a side view of part of a clot retrieval device;

FIG. 21a is an isometric view of part of a clot retrieval device;

FIG. 21b is a detail view of a region of the device of FIG. 21 a;

FIG. 21c is a section through one embodiment of a part of FIG. 21 a;

FIG. 21d is a section through another embodiment of a part of FIG. 21 a;

FIG. 22 is a view of a portion of a clot retrieval device;

FIG. 23 is an isometric view of part of a clot retrieval device;

FIG. 24 is an isometric view of part of another clot retrieval device;

FIG. 25 is a cross sectional view of a portion of the device of FIG. 24; and

FIGS. 26 to 27 are enlarged views illustrating different profiles of corrugations or ribs.

DETAILED DESCRIPTION

Specific embodiments of the present invention are now described in detail with reference to the Figures, wherein identical reference numbers indicate identical or functionality similar elements. The terms “distal” or “proximal” are used in the following description with respect to a position or direction relative to the treating physician. “Distal” or “distally” are a position distant from or in a direction away from the physician. “Proximal” or “proximally” or “proximate” are a position near or in a direction toward the physician.

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Although the description of the invention is in the context of treatment of intracranial arteries, the invention may also be used in other body passageways as previously described.

FIG. 1 is an isometric view of a clot retrieval device 100 with an inner expandable member 101 and outer member 102. In use, inner member 101 creates a flow channel through a clot and its freely expanded diameter is less than that of outer member 102. The inner and outer members are connected at their proximal ends to an elongate shaft 104, whose proximal end 105 extends outside of the patient in use. A distal fragment capture net 103 may be attached to the distal end of the device.

Positional visualization of this device may be provided by a proximal radiopaque coil 109 and distal radiopaque markers 108. User visualization of device 100 would be enhanced by providing visual information to the user on device expansion in a vessel or clot. This information may allow the user to visualise the profile of a clot and provide a fuller map of the luminal space created upon device deployment. As the device is withdrawn, the user will see the device response as it tracks through the anatomy with clot incorporated. It is therefore desirable to add radiopaque materials to outer member 102 and/or to inner tubular member 101 to provide the highest quality information to the user. One of the challenges with incorporating radiopaque material in such a manner is the dampening effect such materials have on superelastic Nitinol. The inventions disclosed in this document facilitate incorporation of radiopaque material and therefore product visualization without compromising the superelastic response of the outer member or inner tubular member. It is intended that any of the designs and inventions disclosed may be adopted to enhance the radiopacity of a clot retrieval device such as shown in FIG. 1, or any clot retrieval device comprising an expandable body.

In the embodiment shown the radiopacity of the outer member is enhanced by the presence of radiopaque elements 107, which are attached to the outer member by supporting fibres 106. These fibres may be connected to the framework of the outer member by a variety of means, including threading the fibres through eyelets or attachment features. Radiopaque elements 107 may comprise tubes, beads or coils of a radiodense material such as Gold, Tungsten, Tantalum, Platinum or alloy containing these or other high atomic number elements. Polymer materials might also be employed, containing a radiopaque filler such as Barium Sulphate, Bismuth SubCarbonate, Barium OxyChloride or Tantalum.

FIG. 2a is an isometric view of a portion of a clot retrieval device 1001 with strut feature 1002 and crown feature 1007 comprising a superelastic material such as Nitinol. The portion of the clot retrieval device is shown is an expanded configuration. It can be appreciated that in the collapsed configuration, for clot retrieval device delivery, the struts 1002 may move to a position adjacent each other. During an interventional procedure, such as a neurothrombectomy procedure, the patient anatomy and device location in visualized with the aid of x-ray equipment such as a fluoroscope. Source x-ray beam 1003 originates at a photon beam source and targets device 1001. Partially scattered x-ray beam 1004 is the photon beam deflected by device 1001 which passes to detector 1008. Partially scattered x-ray beam generically refers to a photon beam which may be absorbed or scattered by a material (e.g. photoelectric absorption or Compton scattering). For materials, such as Nitinol that is relatively non-radiopaque relative to the treatment environment, source photon beams 1004 may pass through the device relatively uninterrupted, without being absorbed, changing trajectory, or without a significant wavelength change.

FIG. 2b is a representation of resulting image 1011 captured by detector 1008 in FIG. 2a . Low contrast image 1013 represents the outline of device 1012 under x-ray. Device 1012 may not be visible or barely visible if it comprises standard material such as Nitinol and/or if device strut feature dimensions are small enough to be below a detectable range. This is due to the level of scattering of the x-ray or photon beam being relatively uninterrupted by device 1012 relative to the tissue environment in which it is placed.

FIG. 2c is an isometric view of a portion of a clot retrieval device 1021 with strut feature 1022 and crown feature 1027 comprising a radiopaque material, or a superelastic material such as Nitinol fully covered with radiopaque material through a process such as electroplating or sputtering. Source x-ray beam 1023 is a source photon beam between and x-ray source and device 1021. Highly scattered x-ray beam 1025 is the photon beam between device 1001 and detector 1008. As an source x-ray beam 1023 passes through radiopaque materials, such as noble metals such as gold, platinum, and the like, the level of scattering of a beam is relatively much greater than the level of scattering of either an adjacent non-radiopaque device comprising Nitinol or relative to the treatment environment where source x-ray beams 1023 pass through relatively uninterrupted.

FIG. 2d is a representation of resulting image 1031 captured by detector 1028 in FIG. 2c . High contrast image 1034 represents the outline of device 1032 under x-ray. Device 1032 is highly visible as it comprises a radiopaque material or material combination such as Nitinol coated with a radiopaque material. This is due to the difference high level of scattering of the x-ray or photon beam, highly uninterrupted by device 1032 relative to the tissue environment in which it is placed.

FIG. 3a is an isometric view of a portion of a clot retrieval device 1041 with strut feature 1042 and crown feature 1047. The device structure substantially comprises superelastic Nitinol material, especially at crown feature 1047 where a high level of elastic recovery is desirable for effective device operation. Discrete radiopaque marker 1045 is located on strut feature 1042 as an example of a location on a structural feature of the device which deflects less and requires less elastic recovery than other features of the device, for example crown feature 1047. Several embodiments of devices incorporating discrete radiopaque marker 1045 are disclosed later. Source x-ray beam 1043 is used to image device 1041 and in this example a mixture of highly scattered x-ray beam 1046 and partially scattered x-ray beam 1044 reach detector 1048.

FIG. 3b is a representation of x-ray image 1051 of device 1052 captured by detector 1048 (FIG. 3a ). Low contrast image 1053 represents areas of device 1041 in FIG. 3a comprising superelastic materials such as Nitinol and high contrast image 1054 represents the location of discrete radiopaque marker 1045 in FIG. 3a which interrupts the path of x-ray source beam 1043. Device 1052 is partially visible to the user as it comprises sections of a radiopaque material and non-radiopaque material. This is due to the difference level of scattering of the x-ray or photon beam, highly uninterrupted by discrete radiopaque marker 1045 relative to the tissue environment and strut feature 1042 and crown feature 1047 comprising superelastic material such as Nitinol which has a partially scattered x-ray beam.

FIG. 4a and FIG. 4b further represent the scattering of x-ray beams and interruption of beam patterns as they pass through a medical device such as a clot retrieval device. FIG. 4a is a cross section view of clot retrieval device 1061 comprising strut feature 1062 with discrete radiopaque marker 1065. Source x-ray beam 1063 passes through the device, and the photon beam reaches x-ray detector 1068 to image device 1061. The wavelength and trajectory of partially scattered photon beam 1066 passed through strut feature 1062 comprising nitinol material without significant disruption. The wavelength and trajectory of highly scattered photon beam 1066 passed through discrete radiopaque marker 1065 is significantly changed or absorbed by said discrete radiopaque marker.

FIG. 4b is an illustration of x-ray image 1071 with low contrast image 1074, high contrast image 1073, and shadow zone 1075. Shadow zone 1075 in FIG. 4b occurs as a result of a mixture of partially scattered photon beams 1064 and highly scattered photon beams 1066 reaching the same area of detector 1068 in FIG. 4 a.

FIG. 5 is a graphical representation of an x-ray image resulting from of two adjacent shadow zones 1085 combining to create an intersection zone 1086.

FIG. 6a is a cross section view of a portion of a clot retrieval device 1091 with strut feature 1092 and a plurality of discrete radiopaque markers 1095. The device structure substantially comprises superelastic Nitinol material, especially strut feature 1092 and especially areas where a high level of elastic recovery is desirable for effective device operation such as crown features not shown in this drawing. A plurality of discrete radiopaque markers 1095 are located on strut feature 1092 as an example of a location on a structural feature of the device which deflects less and requires less elastic recovery than other features of the device. Source x-ray beam 1093 is used to image device 1091 and in this example a mixture of highly scattered x-ray beams 1096 and partially scattered x-ray beam 1094 reach detector 1098 after filtration through an anti-scatter grid.

FIG. 6b is a representation of x-ray image 1101 of device 1092 (FIG. 6a ) captured by detector 1098 (FIG. 6a ). Low contrast image 1104 represents areas of device 1091 in FIG. 6a comprising superelastic materials such as Nitinol and high contrast image 1104 represents the location of discrete radiopaque markers 1095 in FIG. 6a which interrupts the path of x-ray source beam 1043. Shadow Zone 1105 in FIG. 6a corresponds with, referring back to FIG. 6a , a location where a mixture of highly scattered x-ray beams 1096 and partially scattered x-ray beams 1094 reach the same location of x-ray detector 1098. Intersection zone 1106 in FIG. 6b represents a zone where, referring back to FIG. 6a , a mixture of highly scattered x-ray beams 1096 and partially scattered x-ray beams 1094 reach the same location of x-ray detector 1098 in a region where discrete radiopaque markers 1095 are located in relatively close proximity. The configuration has the advantage of creating the illusion for the user of a continuous marker under x-ray imaging, thereby providing fuller information on the geometry of the device.

FIG. 7a and FIG. 7b are respective isometric and developed plan views of a repeating pattern of clot retrieval device 1201, comprising strut features 1202 and crown features 1203. Clot retrieval device has an expanded configuration as shown in FIGS. 7a and 7b and a collapsed configuration for delivery. In the collapsed configuration areas of high strain, preferably high elastic strain, are concentrated at crown features 1203. Force is transmitted to crown features 1203 via structural strut features 1202. Low strain, preferably low elastic strain, regions are concentrated in strut features 1202.

FIG. 8 is a developed plan view of a portion of another clot retrieval device 1301, comprising strut features 1302 and crown features 1303. In this embodiment, discrete elongate radiopaque markers 1304 are located in strut features 1302, and undergo low levels of strain as clot retrieval device 1301 moves from a collapsed to an expanded configuration. As described previously, radiopaque markers generally comprise noble metals which have lower yield points and therefore reduced elastic recovery in contrast to a superelastic material such as Nitinol.

FIG. 9 is developed plan view of another clot retrieval device 1401 comprising crown features 1403, strut features 1402, discrete radiopaque markers 1404, and inter-marker strut region 1405. In this embodiment, limitations associated with conflicting requirements of highly recoverable elastic strain and incorporating radiopaque features to optimise visibility are overcome. The location of discrete radiopaque markers 1404 in low strain strut features 1402 away from high strain location crown features 1403 reduces overall plastic strain and spacing discrete radiopaque markers apart in a strut to create inter-marker strut regions 1405 further reduces accumulated plastic strain to optimise device operation, particularly in moving from a collapsed configuration to an expanded configuration and transmission of force by clot retrieval device 1401 in a radial direction, which is desirable for effective clot retrieval. Referring back to FIGS. 6a and 6b , it will be appreciated that spacing marker bands apart will provide high quality visual information to the user due as high contrast regions are created both from radiopaque markers and from combined shadow zones where radiopaque markers are located adjacent each other.

FIG. 10a is a sectioned plan view of a portion of partially coated clot retrieval device 1501 having crown feature 1510, uncoated strut feature 1516, and partially coated strut feature 1511 partially covered in a radiopaque coating 1515. The strut and crown features may comprise a highly elastic material such as Nitinol, and the radiopaque material may comprise noble metals such as gold or platinum or the like or a polymer material such as polyurethane, pebax, nylon, polyethylene, or the like, filled with radiopaque filler such as tungsten, barium sulphate, bismuth subcarbonate, bismuth oxychloride or the like or an adhesive filled with radiopaque filler. Strut features and crown features may comprise Nitinol material with strut sidewall recess feature 1512. In the example shown, strut sidewall recess feature comprises a series of grooves in the sidewall of the strut. Grooves may be incorporated in a sidewall using cutting process such as laser cutting or other cutting means of incorporated through mechanical abrasion, cutting, grinding, or selective chemical etching. Other recess features may be incorporated such as dimples, knurls, or highly roughened surface to achieve a non-planar, textured, or rough surface. The coating can be applied as a single step (a partially coated device is shown for illustration purposes) through a process such as electroplating, sputtering, dipping, spraying, cladding, physical deposition, or other means.

FIG. 10b is a detailed view of partially coated strut feature 1511 showing uncoated groove 1512 for illustration purposes on one side and coating 1515 on the other side. Device 1501 has strut sidewall recess feature 1512 and device 1501 is preferentially coated in these areas with thick coating section 1513 resulting, which is located in a low-strain area for effective operation. The elastic recovery dampening effect of coating material 1515 has less impact on low strain strut features. Crown feature 1510 has a thin coating 1514 and is less preferentially coated because of its non-recessed, non-textured, or smooth surface, so potential dampening effect of radiopaque coating is minimised in parts of the clot retrieval device 1501 features requiring more elastic recovery such as crown feature 1510.

FIG. 10c is a partially cut isometric view of clot retrieval device 1501. The device is shown with coating 1515 partially cut away for illustration purposes. Clot retrieval device 1501 has crown features 1510, uncoated strut feature 1516 with strut sidewall recess feature 1512 to promote thick coating layer 1513 in on low strain parts of the device and thin coating layer 1514 on high strain parts of the device.

FIG. 11 is an isometric view of a repeating cell of clot retrieval device 1601 comprising crown feature 1602 and strut feature 1603. Strut feature 1603 has top surface grooves 1604 to promote preferential radiopaque coating adherence now on the top surface in a similar manner to preferential coating deposition or adherence described previously.

FIG. 12 is an isometric view of a repeating cell of clot retrieval device 1701 comprising crown feature 1702 and strut feature 1703. Strut feature 1703 has top surface dimples 1704 to promote preferential radiopaque coating adherence on the top surface in a similar manner to preferential coating deposition or adherence described previously. Grooves 1604 or dimples 1704 in FIG. 11 and FIG. 12 respectively may be added through processing techniques such as laser ablation, laser cutting, mechanical abrasion such as grinding, mechanical deformation process such as knurling or indentation and the radiopaque covering described previously.

FIG. 13a is an isometric view of tubing 1801 comprising Nitinol material 1803 and radiopaque cladding 1802 comprising a radiopaque material such as a gold, platinum, iridium or tantalum. This material may be processed by means such as electroplating, sputtering, or a mechanical compression process such as crimping or drawing.

FIG. 13b is an isometric view of tubing 1806 with comprising Nitinol material 1803 and cladding 1302 comprising rings of radiopaque material, with intermittent gaps 1304 between cladding rings 1302. Tubing 1806 may be manufactured from applying a secondary process to tubing 1801 in FIG. 13a by removing annular sections of radiopaque material through a process such as laser ablation, laser cutting, or mechanical removal such as grinding or cutting for example on a lathe.

FIG. 14 is an isometric view of clot retrieval device 1901. Clot retrieval device 1901 may be constructed of tubing 1806 as shown in FIG. 13. Device 1901 may be made through a series of processing steps wherein tubing 1806 is cut to form strut and crown patterns, deburred, expanded and heat treated, and electropolished. Crown features 1903, which are areas requiring high elastic recovery, are located in areas in which cladding 1902 is absent, and strut feature 1904, which undergoes less strain and requiring less elastic recovery, is located in areas where cladding 1902 remains.

FIG. 15 is an isometric view of clot retrieval device 2001 with radiopaque material free crowns 2003 as in device 1901 of FIG. 14 but the spacing of cladding rings in device 2001 is such that strut 2004 also has clad-free areas 2005 to further promote elastic behaviour of strut feature 2004. In transitioning from collapsed configuration to expanded configuration or vice versa, areas of high strain are located at crown feature 2003 and elastic recovery is less of a requirement for strut features 2004. It may however by desirable in use, particularly if a device is required to conform to a tortuous vessel such in use, for strut feature 2004 to deflect in bending and recover elastically. Device 2001 with radiopaque-material-free areas 2005 has the advantage of facilitating more recoverable strain. Devices 2001 and 1901 may be manufactured from clad tubing 1806 and cutting a pattern whereby crown features and strut features are located in clad-free and clad areas respectively, they may also be constructed from tubing 1801 and cladding removed during or subsequent to the laser cutting process.

FIG. 16 is an isometric view of clot retrieval device 2101 comprising crown features 2102 and strut features 2105. In this case the clot engaging framework is formed for example by laser cutting from a tube of uniform wall thickness. Strut 2105 comprises widened strut sections 2104 and regular strut sections 2103, which respectively provide enhanced radiopacity and flexibility. Radiopacity of device 2101 is enhanced by the addition of widened strut sections 2104 in strut feature 2105. The increased material volume in the widened strut section 2104 blocks x-ray/photon beams in contrast to crown feature 2102 and regular strut section 2013 without compromising device flexibility performance.

A particular advantage of this design is that effective radiopacity may be achieved through the addition of a much lower volume of radiopaque material than would otherwise be possible. For example, if an endovascular medical device comprised a Nitinol strut of width and thickness of between 50 and 100 microns approximately, such a strut would typically be very difficult for a physician to see under fluoroscopy. If portions of such a strut were made wider as per sections 2104 of FIG. 16, these widened sections would create a greater surface area and might somewhat improve visibility under fluoroscopy. If such a strut with widened sections were coated with a radiopaque material (such as any of those previously mentioned) it could be rendered highly visible under fluoroscopy, and because of the greater surface area of the widened regions 2104, a lesser thickness of radiopaque coating would be needed to make such a device radiopaque than would be the case if the widened sections were absent. Thus a device with such widened strut features can be rendered radiopaque with significantly reduced adverse damping effects. The width of the widened sections will directly affect the resultant radiopacity of the device, and will ideally be greater than 150 microns, and more preferably greater than 200 microns. Thus the width of the widened sections will typically be greater than 1.5 times that of the strut, and preferably 2 or more times that of the strut. In order to minimize impact on the wrapped profile of the device the widened areas will be staggered on adjacent struts, so that they do not contact each other when the device is in the collapsed state. The shape of the widened sections may (in plan view) be circular or elliptical or square or rectangular or any shape that serves to increase the surface of the strut and hence increase visibility. In one embodiment a hole or eyelet is provided within the widened area, which could serve as an attachment point for another component, or simply serve to remove mass from the device and enhance flexibility. Any number of widened areas may be provided on a device or strut, but ideally two or more widened areas are provided so that visual information is provided to the observer of the condition as well as the position of the strut in question.

The widened portion of the strut may be at least 50%, optionally at least 75%, optionally at least 100%, optionally at least 125%, optionally at least 150%, optionally at least 175%, optionally at least 200%, optionally at least 300% wider than the regions along the length of the strut between the widened portions.

The widened portions may have a length which is less than 100%, optionally less than 75%, optionally less than 50%, optionally less than 25% of the length of the regions of the strut between the widened portions.

The length of the regions of the strut between the widened portions may be greater than 300%, optionally greater than 400%, optionally greater than 500%, optionally greater than 600%, optionally greater than 700%, optionally greater than 800%, optionally greater than 900% of the width of the strut.

FIG. 17a is a cross section of a structural element 2204 in a non-strained condition of clot retrieval device 2201 comprising Nitinol material, with radiopaque material coating 2202. Line 2203 represents a line or plane within structural element 2204 away from the neutral axis of bending.

FIG. 17b is a cross section of structural element 2204 in a strained configuration through a bending load.

FIG. 18a is a cross section of structural element 2304 of clot retrieval device 2301 comprising superelastic material such as Nitinol and discontinuous radiopaque coating 2302. Line 2303 is a reference line close to device surface away from the neutral axis of structural element 2304. In FIG. 18b , structural element 2304 is shown in the deformed or bent configuration with line 2303, which is between the neutral axis and the outer surface, representing a line or plane of constant strain. Discontinuous radiopaque coating 2302 may be deposited through means such as a sputter coating process, growing single crystals on the surface in a discrete fibre-like micro or nano-structure or columnar structure. Other means of achieving discontinuous radiopaque coating include micro-laser ablation of layers or mechanical separation such as slicing. One advantage of such a coating structure is that a high strain (or deformation) can be induced in the substrate material without a high strain being induced in the coating material. This is because the discrete micro-fibres or micro-columns from which the coating is composed have minimal connectivity between each other. Thus the outer ends of the micro-fibres or micro-columns simply move further apart when a convex bend is applied to the substrate material as shown in FIG. 18b . A smooth surface may subsequently be achieved on the device by coating with a polymer coating, such as a layer of Pebax for example, or Parylene, or a hydrophilic material and/or a hydrogel.

Deformation, such as the applied bending load shown in FIG. 17 by way of example, causes material to deform in tension along line 2203. For materials such as Nitinol, the stress-strain or force-deflection deformation generally follows a curve shown in FIG. 19a where material along line 2204 starts at point A in and follows the arrows to generate a typical flag-shaped stress-strain curve. Stress or force is shown on the y-axis and strain or deflection is shown along the x-axis of FIG. 19. When an applied load or deflection is removed, for nitinol, the load is reversed at point R and the material follows the unloading curve shown until it reaches point B. For a perfectly elastic of pseudoelastic material, point A and point B are coincident and there is no residual or plastic strain in the material, and therefore no permanent deformation.

Referring now to FIG. 19b , a pattern of stress-strain is shown which is more typical of a radiopaque material such as gold, where loading begins at point A and the stress-strain behaviour follows the loading pattern shown until the load is removed and the strain reduces to point B. Since point A and point B are not coincident, plastic or permanent deformation results, which is quantified as the distance between point B and point A. Considering the structural element 2201 comprising material such as Nitinol combined with radiopaque material such as Gold, the loading and unloading pattern is illustrated in FIG. 19c wherein load or strain is applied, and when the load is removed at point R, the internal material stress-strain response follows the curve from point R to point B. The combined material properties are such that plastic strain, defined by the distance between B and A along the x-axis, results. In this configuration the plastic strain is less than that of pure radiopaque material but more than that of pure Nitinol. The dampening effect on device recovery is generally not desirable for effective operation of clot retrieval device performance.

FIG. 19d is a stress-strain curve of structural element 2301 in bending, taking line 2303 as an example, where the device is loaded from point A to point R and when the load is removed the device unloads from point R to point B. The magnitude of plastic strain is reduced (reduced distance between point B and A when comparing FIGS. 19c and 19d ) as the coating becomes more discontinuous, and approaches zero as the number of discontinuities increases.

FIG. 20a is a side view of clot retrieval device outer member 2401 comprising strut features 2402 and crown features 2403. Radiopaque filaments 2405 are connected between crown features or strut features to enhance device radiopacity. Radiopaque filaments are located along the outer circumference of clot retrieval device outer member 2401 in order to enhance fluoroscopic visualisation of the expanded or collapsed configuration of the device. The circumferential location of the filaments may also aid visualisation of device interaction with a clot during use. The filaments may run parallel to the axis of the device, or in a helical path from crown to crown, crown to strut, or strut to strut in order to maintain clot reception space 2406 for clot retrieval. Radiopaque filaments may comprise single of multiple strands of radiopaque wire such as tungsten, platinum/iridium or gold, or similar materials.

FIG. 20b is a side view of clot retrieval device outer member 2501 comprising strut features 2502 and crown features 2503. Filaments 2505 incorporating radiopaque beads 2506 are connected between crown features or strut features to enhance device radiopacity. Sequenced radiopaque beads 2505 along filaments 2505 do not contribute to the mechanical stiffness of the device or contribute to or detract from radial force in any way, and in a collapsed configuration wrap into inter-strut spaces in a versatile manner. The filaments may run parallel to the axis of the device, or in a helical path from crown to crown, crown to strut, or strut to strut in order to maintain clot reception space 2507 for clot retrieval as in FIG. 20a . While radiopaque beads are spaced apart to maintain beaded-filament flexibility, adjacent beads create the illusion of a continuous radiopaque member, providing high quality visual information to the user. Filaments may comprise high ultimate tensile strength monofilament or multifilament polymers such as UHMWPE, Kevlar, aramid, LCP, PEN or wire such as Nitinol and radiopaque beads may comprise polymer filled with radiopaque filler such as tungsten powder, barium sulphate, of solid radiopaque material such as gold or platinum.

FIG. 20c is a side view of clot retrieval device outer member 2601 comprising strut features 2602 and crown features 2603. Filaments 2605 are incorporated in device outer member 2601 in a similar matter detailed in FIG. 20b , with radiopaque coils 2608 located on filament 2605. Radiopaque coils may comprise wound wire such as platinum/iridium or platinum/tungsten or similar radiopaque wire wound into a spring-like coil structure. Filaments 2605 incorporating radiopaque coils 2608 maintain flexibility in bending so device performance characteristics such as flexibility, trackability, radial force, deliverability, etc. are not compromised.

FIG. 21a is an isometric view of clot retrieval device outer member 2701 comprising strut features 2702 and crown features 2703. An elongate radiopaque thread 2405 is incorporated in the structural elements, i.e. struts or crowns, of clot retrieval device outer member. Elongate radiopaque thread 2704 threads the perimeter of outer member 2704 to define the outer boundary of device in an axial and circumferential direction under fluoroscopic imaging. A plurality of radiopaque threads may be incorporated to further define the boundary of the outer member.

FIG. 21b illustrates a means of incorporating elongate thread 2804 in strut 2802 through eyelet 2805. Elongate radiopaque thread may be incorporated through other means such as surface adhesion.

FIG. 21c and FIG. 21d are cross section views of bifilar elongate radiopaque threads 2901 and 3001 respectively incorporated in outer member 2701 in FIG. 21a . Thread 2904 is a single material radiopaque thread such as platinum/iridium, platinum/tungsten, or gold. Thread 3001 in FIG. 21d comprises Nitinol outer material 3003 with inner radiopaque core such as a gold core. The coaxial configuration of radiopaque thread 3001 part retains the elasticity/elastic recovery, in particular at low strains, and has the advantage of contributing to the structural integrity of clot retrieval device 2701, for example it may be used to enhance the radial force of the device. The bifilar configuration of thread 2901 enhances radiopacity by increasing the effective area or volume of material scattering the x-ray field while maintaining good flexibility.

FIG. 22 is a plan view of clot retrieval device cell 3101 comprising structural strut 3102 and structural crown 3102 with radiopaque markers 3106 traversing cell 3101, connected via non-structural struts 3107. Non-structural struts 3107 are connected to structural struts 3102 at connection crown 3105, and have minimal structural integrity and therefore minimal contribution to the structural rigidity in bending and in the radial direction. The cell may comprise a Nitinol material with radiopaque markers incorporated in eyelets using a crimping process.

FIG. 23 is an isometric view of clot retrieval device cell 3201 comprising crown features 3203 and strut features 3202. A radiopaque filament 3204 is threaded through side holes 3205 in strut 3202. Side holes 3205 facilitate incorporation of radiopaque filament in inter-strut space, therefore not adding to the outer or inner profile of the device. Radiopaque filament may comprise radiopaque material, or polymer or wire monofilaments or yarns with radiopaque beads or coils described previously.

FIG. 24 is an isometric view of a portion of clot retrieval device 3301 comprising crown features 3303 and strut features 3302. Strut 3302 comprises thickened strut sections 3304 which provide enhanced radiopacity through the additional material volume and surface area provided. In one embodiment the device 3301 also compromises a radiopaque coating, which covers some or all of the outer surface of the device. This coating may be one of the various coatings previously described herein. In one preferred embodiment the clot retrieval device is made of Nitinol and the radiopaque coating is Gold. In the most preferred version of this embodiment the Gold coating is applied by a sputter coating or plasma deposition process, rather than by an electroplating process. A strike layer may be placed between the Gold radiopaque layer and the Nitinol to improve adhesion.

In the embodiment shown the sidewalls 3307 of struts 3302 and crown features 3303 are profiled with a corrugated shape 3305. This corrugated shape serves to increase the surface area of the device and helps to reduce the damping effect of the radiopaque coating on the recovery of the Nitinol device. When device 3301 is wrapped down for delivery, the struts and crowns deform and bend. As the struts bend the side walls either elongate or compress depending on whether they are in tension or compression. The strain induced by this elongation or compression can cause plastic deformation in the radiopaque coating if it is greater than the elastic strain limit of the material, which is typically less than 1%. However the corrugated surface has the effect of increasing the effective length of the side wall of the strut and thus reducing the effective strain on the radiopaque coating, so that the damping effect can be reduced or eliminated.

FIG. 25 shows one embodiment of a section view through strut 3302 of FIG. 24. Strut 3302 is comprised of a Nitinol core 3309 and a radiopaque coating 3308. In this embodiment the top surface 3306 of strut 3302 has a corrugated profile 3310, providing an additional damping reduction to that described for the side walls above.

FIGS. 26 and 27 show alternative corrugation profiles 3331 and 3351, which might be adopted in place of corrugations 3305 and 3310 shown in FIGS. 24 and 25.

Modification and additions can be made to the embodiments of the invention described herein without departing from the scope of the invention. For example, while the embodiments described herein refer to particular features, the invention includes embodiments having different combinations of features. The invention also includes embodiments that do not include all of the specific features described.

The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail. 

The invention claimed is:
 1. A clot retrieval device comprising an elongate shaft and an expandable clot engaging element on the shaft, the clot engaging element comprising a framework formed from a substrate material and having a plurality of sequentially spaced struts and crowns, wherein to provide enhanced radiopacity, each strut comprises a plurality of widened portions each separated by a narrower regular strut section, wherein each widened portion is at least 50% wider than the narrower regular strut section along a length of the strut between the widened portions.
 2. The clot retrieval device as claimed in claim 1 wherein the widened portion of the strut is at least 75%, at least 100%, at least 125%, at least 150%, at least 175%, at least 200%, at least 300% wider than the narrower regular strut section along a length of the strut between the widened portions.
 3. The clot retrieval device as claimed in claim 1 wherein the widened portions have a length which is less than 100%, less than 75%, less than 50%, less than 25% of a length of the narrower regular strut section.
 4. The clot retrieval device as claimed in claim 1 wherein the length of the regions of the strut between the widened portions is greater than 300%, greater than 400%, greater than 500%, greater than 600%, greater than 700%, greater than 800%, greater than 900% of the width of the strut.
 5. The clot retrieval device as claimed in claim 1 wherein the clot engaging element is cut from a tube of uniform thickness.
 6. The clot retrieval device as claimed in claim 1 wherein at least a portion of the framework is coated with a radiopaque material.
 7. The clot retrieval device as claimed in claim 6 wherein the coating material is Gold, Tantalum, Tungsten, Platinum or an alloy of one of these elements or other dense element or alloy containing one or more radiodense elements.
 8. The clot retrieval device as claimed in claim 6 wherein the coating material comprises a polymer or adhesive filled with a dense or high atomic number material such as Barium Sulphate, Bismuth SubCarbonate, Barium OxyChloride, Gold, Tungsten, Platinum or Tantalum.
 9. The clot retrieval device as claimed in claim 6 wherein the coating material is applied using an electroplating process, a dipping process, a plasma deposition process, an electrostatic process, a dip or spray coating process, a sputtering process, a soldering process, a cladding process or a drawing process.
 10. The clot retrieval device as claimed in claim 1 wherein the substrate material has a density of less than 10 g/cm³, optionally less than 8 g/cm³.
 11. The clot retrieval device as claimed in claim 1 wherein the substrate material is a superelastic material such as Nitinol or other super or pseudo elastic metallic alloy.
 12. A clot retrieval device comprising an elongate shaft and an expandable section, the expandable section comprising a framework of sequentially spaced strut elements and connections between the strut elements, the framework being formed from a substrate material, wherein to provide enhanced radiopacity, each strut element comprises a plurality of widened portions each separated by a narrower regular strut section, wherein each widened portion is at least 50% wider than the narrower regular strut section along a length of the strut between the widened portions.
 13. The clot retrieval device as claimed in claim 12 wherein the connections comprise crown elements.
 14. The clot retrieval device as claimed in claim 13 comprising a second coating on at least portion of the crown elements.
 15. The clot retrieval device as claimed in claim 13 comprising a first coating on the strut elements and a second coating on the crown elements.
 16. The clot retrieval device as claimed in claim 15 wherein the first and second coatings are of the same material.
 17. The clot retrieval device as claimed in claim 15 wherein the first and second coatings are of different materials.
 18. The clot retrieval device as claimed in claim 17 wherein at least a portion of the framework is coated with a radiopaque material such as gold.
 19. The clot retrieval device as claimed in claim 15 wherein the thickness of the first coating varies along a length of a strut element.
 20. The clot retrieval device as claimed in claim 12 comprising a first coating on at least portion of the strut elements. 